Variable Displacement Variable Pressure Vane Pump System

ABSTRACT

A variable displacement variable pressure vane pump system provides lubrication oil to a mechanical system. The system has a first control mechanism, which can be a control chamber directly acting on the control slider or a control chamber and control cylinder which acts on the control slider and a second control mechanism which is a control chamber and control cylinder which acts on the control slider. A control valve, operated by an engine control unit or other suitable control mechanism, selectively provides pressurized lubrication oil to the second control mechanism to allow the output of the pump system to more closely match the requirements of the mechanical system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/161388, filed on Jul. 18, 2008, which is a National Phase ofPCT/CA2007/000118, filed Jan. 31, 2007, which claims the benefit of U.S.Provisional Application No. 60/763720, filed Jan. 31, 2006. The entiredisclosures of each of the above applications are incorporated herein byreference.

FIELD

The present invention relates to variable displacement vane pumps. Morespecifically, the present invention relates to a variable displacementvariable pressure vane pump system for mechanical systems such asinternal combustion engines or automatic transmissions.

BACKGROUND

Mechanical systems such as internal combustion engines and automatictransmissions typically include a lubrication pump to providelubricating oil, under pressure, to many of the moving components and/orsubsystems of the mechanical systems. In most cases, the lubricationpump is driven by a mechanical linkage to the mechanical system and thusthe operating speed, and output, of the pump varies with the operatingspeed of the mechanical system. While the lubrication requirements ofthe mechanical system also vary with the operating speed of themechanical system, unfortunately the variation in the output of the pumpand the variation of the lubrication requirements of the mechanicalsystem are generally nonlinear. The difference in these requirements isfurther exacerbated when temperature related variations in the viscosityand other characteristics of the lubricating oil are factored in.

To deal with these differences, prior art fixed displacement lubricatingpumps were generally designed to operate effectively at high, ormaximum, oil temperatures, resulting in an oversupply of lubricating oilat most mechanical system operating conditions and a waste, or pressurerelief, valve was provided to “waste” the surplus lubricating oil backinto the pump inlet or oil sump to avoid over pressure conditions in themechanical system. In some operating conditions such as low oiltemperatures, the overproduction of pressurized lubricating oil can be500% of the mechanical system's needs so, while such systems workreasonably well, they do result in a significant energy loss as energyis used to pressurize the unneeded lubricating oil which is “wasted”through the relief valve.

More recently, variable displacement vane pumps have been employed aslubrication oil pumps. Such pumps generally include a control ring, orother mechanism, which can be moved to alter the displacement of thepump and thus its output at an operating speed. Typically, a feedbackmechanism, in the form of a piston or control chamber supplied withpressurized lubricating oil from the output of the pump, either directlyor via an oil gallery in the mechanical system, alters the displacementof the pump to avoid over pressure situations in the engine over theexpected range of operating conditions of the mechanical system. Anexample of such a pump is shown in U.S. Pat. No. 4,342,545 to Schuster.

While such variable displacement pumps provide some improvements inenergy efficiency over fixed displacement pumps, they still result in asignificant energy loss as they must still be designed to provide oilpressures which meet the highest expected mechanical system requirementsand operating temperatures, even when the mechanical system operatingconditions normally do not necessitate such high requirements.

SUMMARY

It is an object of the present invention to provide a novel variabledisplacement variable pressure vane pump which obviates or mitigates atleast one disadvantage of the prior art.

According to a first aspect of the present invention, there is provideda variable displacement variable pressure vane pump system for providinglubrication oil to a mechanical system comprises: a variabledisplacement variable pressure vane pump having a control slider whichis moveable to alter the displacement of the pump; a biasing means tobias the control slider towards a position corresponding to the maximumdisplacement position of the pump; a first control mechanism responsiveto the pressure of the lubrication oil output from the pump to apply aforce to the control slider to counter the biasing force of the biasingmeans and to urge the control slider away from the positioncorresponding to the maximum displacement position of the pump; a secondcontrol mechanism responsive to the pressure of the lubrication oiloutput from the pump to apply a force to the control slider to counterthe biasing force of the biasing means and to urge the control slideraway from the position corresponding to the maximum displacementposition of the pump; and a control means operable to vary thelubrication oil supplied to the second control mechanism to alter theoutput of the pump to more closely correspond to the lubricationrequirements of the mechanical system.

The present invention provides a variable displacement variable pressurevane pump system for providing lubrication oil to mechanical systemssuch as internal combustion engines and/or automatic transmissions. Thesystem includes at least a first control mechanism, which can be acontrol chamber directly acting on the control slider or a controlchamber and control cylinder which acts on the control slider and asecond control mechanism which is a control chamber and control cylinderwhich acts on the control slider. A control valve, operated by an enginecontrol unit or other suitable control mechanism, can selectively varypressurized lubrication oil to the second control mechanism to allow theoutput of the pump system to more closely match the requirements of themechanical system. In one embodiment, the control mechanism merelyapplies or removes pressurized lubrication oil and in anotherembodiment, the control mechanism can control the pressure of thepressurized lubrication oil provided to the second control mechanism. Inanother embodiment a third control mechanism, which is a control chamberand control cylinder which acts on the control slider, is provided toprovide finer granularity in controlling the output of the pump systemto more closely correspond to the lubrication requirements of theengine. In yet another embodiment, both the first and second controlmechanisms are control chambers and control cylinders which act on thecontrol slider.

DRAWINGS

Preferred embodiments of the present invention will now be described, byway of example only, with reference to the attached Figures, wherein:

FIG. 1 shows an example of a plot of the oil pressure demand of amechanical system versus the output of a prior art lubricating pump;

FIG. 2 shows a hydraulic circuit of a variable displacement variablepressure vane pump system in accordance with the present invention withthe pump system in a lower speed, higher displacement and low pressurestate;

FIG. 3 shows the pump system of FIG. 2 in a lower speed, lowdisplacement and low pressure state;

FIG. 4 shows the pump system of FIG. 2 in a higher speed, highdisplacement and high pressure state;

FIG. 5 shows the pump system of FIG. 2 in a higher speed, lowdisplacement and high pressure state;

FIG. 6 shows an example plot of oil pressure demand of a mechanicalsystem versus the output of the pump system of FIGS. 2 through 5;

FIG. 7 shows a hydraulic circuit of another variable displacementvariable pressure vane pump system in accordance with the presentinvention wherein the output of the pump is directly fed to the controldevices;

FIG. 8 shows another hydraulic circuit for the pump system of FIGS. 2through 5;

FIG. 9 shows a hydraulic circuit of another embodiment of a variabledisplacement variable pressure vane pump system in accordance with thepresent invention with the pump system in a high displacement state;

FIG. 10 shows a plot of oil pressure demand of a mechanical systemversus the output of the pump system of FIG. 9;

FIG. 11 shows a hydraulic circuit of another embodiment of a variabledisplacement variable pressure vane pump system in accordance with thepresent invention with the pump system in a lower speed, highdisplacement and lower pressure state;

FIG. 12 shows a hydraulic circuit of another embodiment of a variabledisplacement variable pressure vane pump system in accordance with thepresent invention with the pump system in a high displacement state; and

FIG. 13 shows a hydraulic circuit of another embodiment of a variabledisplacement variable pressure vane pump system in accordance with thepresent invention with the pump system in a high displacement state.

DETAILED DESCRIPTION

FIG. 1 shows a typical plot of the lubricating oil pressure requirement(shown in solid line) of a mechanical system, such as a typical internalcombustion engine, versus the output (shown in dashed line) of a priorart variable displacement pump, such as the pump taught in theabove-mentioned Schuster patent. The corner on the output (dashed line)results from the movement of the control slide by the control piston toreduce the displacement of the pump as the output of the pump reaches apreset value. The shaded area between the engine demand curve and thepump output curve represents the engine operating conditions whereinenergy is lost as the pump pressure output exceeds engine demand.

A lubrication pump system in accordance with the present invention isindicated generally at 20 in FIG. 2. While in the following discussionthe lubrication needs of an internal combustion engine are discussed,the present invention is not so limited and the present invention can beadvantageously employed with a variety of mechanical systems includinginternal combustion engines, automatic transmission systems, etc.

System 20 includes a Variable Displacement Vane Pump (VDVP) 24, whichcan be any suitable VDVP, such as one similar to that taught in theabove-mentioned U.S. Patent to Schuster. VDVP 24 includes a rotor 28,which is driven by the internal combustion engine on which pump system20 is installed. Rotor 28 includes a set of radially extending vanes 32which engage the inner surface of a control slider 36 which can be movedabout a pivot point 38 to alter the eccentricity between the rotor andvanes and the inner surface of control slider 36, thus altering thedisplacement of VDVP 24.

VDVP includes a biasing spring 40 which biases control slider 36 to themaximum displacement position and a control piston 44 is provided to,under certain conditions, move control slider 36, against the bias ofbiasing spring 40, towards the minimum displacement position.

VDVP 24 includes an inlet 48 which is in fluid communication with asource 52 of lubricating oil, such as the sump of an engine and anoutlet 56 which supplies pressurized lubricating oil to the engine,normally through an oil filter 60. In the case of clean oil actuation,where the oil has passed through filter 60, pump outlet 56 is connectedto an overpressure relief valve 64 which opens to return somelubricating oil to source 52 if the output pressure of VDVP 24 exceeds apre-selected pressure in order to protect oil filter 60. If theactuation is performed with unfiltered oil, directly from pump outlet56, the circuit feedback is direct, as described below with respect tothe embodiment of FIG. 7, allowing the omission of overpressure reliefvalve 64.

As shown, chamber 68 at one end of control piston 44 is in fluidcommunication with the pressurized lubricating oil supplied to theengine and the force developed on control piston 44 in chamber 68, whichincreases with the pressure of the lubricating oil, moves control slide36 against biasing spring 40 to reduce the displacement of VDVP 24 andhence reduce the output flow.

As will be apparent to those of skill in the art, the components ofsystem 20 described so far, and in particular biasing spring 40 andcontrol piston 44, are conventional and would result in VDVP 24operating in much the same manner as illustrated in the plot of FIG. 1.

However, unlike conventional lubricating pumps (like the pump taught inSchuster) and conventional pump systems, VDVP 24 further includes acontrol chamber 72 formed between the interior wall of the pump housingof VDVP 24, pivot point 38, slider seal 74 and the outer surface ofcontrol slider 36 on the same side of pivot point 38 as control piston44. Control chamber 72 is in fluid communication with a control valve 76which is, in turn, in fluid communication with a source of pressurizedlubricating oil from an engine gallery, oil line or any other suitablesource of pressurized lubricating oil supplied from VDVP 24 and whichhas a return line 78 to source 52 to relieve pressure in control chamber72 when control valve 76 is in the appropriate position.

Volume 80, formed between the interior wall of the housing of VDVP 24,pivot point 38, slider seal 74 and the outer surface of control slider36 on the same side of pivot point 38 as biasing spring 40, issubstantially sealed from the pressurized lubricating oil and is influid communication with source 52 and is thus maintained at, or closeto, atmospheric pressure.

As should now be apparent to those of skill in the art, when controlchamber 72 is supplied with pressurized lubricating oil, a force isdeveloped by this lubricating oil on control slider 36. The forcedeveloped by chamber 72 adds to the force developed by control piston 44and the resulting sum of these forces acts against the biasing force ofbiasing spring 40, moving control slider 36 to reduce the displacementof VDVP 24 to a greater extent than would be the case if just the forceof control piston 44 was applied.

Preferably, the projected area of control chamber 72 (i.e.—the area ofcontrol chamber 72 over which the pressure of the lubrication oilgenerates a force on control slider 36) is much larger than theprojected area of control piston 44. Thus, at lower operating speeds,control chamber 72 will generate larger forces on control slider 36, tocounter the biasing force of biasing spring 40, than the forces that aredeveloped by control piston 44. This arrangement allows a reduced sizeof VDVP 24, biasing spring 40 and control piston 44 thus reducing theweight and cost of VDVP 24.

Control valve 76 can selectively apply or remove pressurized fluid inresponse to any suitable control mechanism. In the illustratedembodiment, control valve 76 is controlled via a solenoid which iselectrically actuated by a signal from the engine controller unit (ECU)which knows the engine operating speed and, in many cases, will alsoknow at least some measure of the load on or temperature of the engine,and will actuate control valve 76 to decrease or increase thedisplacement of VDVP 24 as necessary to provide the designed oilpressure at different engine operating conditions.

System 20 is not limited to control valve 76 being controlled by theECU, nor to control valve 76 being electrically controllable, althoughboth of these are presently preferred, and control valve 76 can beoperated by any suitable means as will occur to those of skill in theart.

As should now be apparent, in FIG. 2 system 20 is illustrated in a lowerspeed range, maximum displacement configuration wherein the forcedeveloped, due to oil pressure output from VDVP 24, in chamber 68 and incontrol chamber 72 act to move control slider 36 from the maximumdisplacement position and, due to the operating speed of VDVP 24, thisforce is insufficient to counter the biasing force of biasing spring 40.

FIG. 3 shows system 20 in a low speed range, minimum displacementconfiguration. As illustrated, despite the relatively low speed (buthigher speed than that of the configuration of FIG. 2) at which VDVP 24is operating, control slider 36 has been moved against the biasing forceof biasing spring 40 by the combined forces generated in chambers 68 andchamber 72.

FIG. 4 shows system 20 in a high speed range, maximum displacementconfiguration. As illustrated, control valve 76 has been moved todisconnect the pressurized lubricating oil from control chamber 72 andto allow the pressure of the lubricating oil in control chamber 72 toreturn to source 52 through return line 78. Thus, control piston 44exerts the only substantial force on control slider 36 to counter thebiasing force of biasing spring 40 and this force is insufficient tocounter the biasing force of biasing spring 40.

FIG. 5 shows system 20 in a high speed, minimum displacementconfiguration wherein control valve 76 is in the same position as inFIG. 4, removing the pressure from control chamber 72. However, due tothe relatively high operating speed of VDVP 24, the pressure of thelubricating oil in chamber 68 develops sufficient force on controlpiston 44 to move control slider 36 to the illustrated minimumdisplacement position against the biasing force of biasing spring 40.

FIG. 6 shows a plot, similar to that of FIG. 1, of the lubricating oilpressure requirement (shown in solid line) of a typical internalcombustion engine versus the output (shown in dashed line) of anembodiment of system 20. System 20 is in the: low speed, maximumdisplacement configuration of FIG. 2 in the region of the plot indicatedby reference numeral 90; low speed, reduced displacement configurationsimilar to that of FIG. 3 in the region of the plot indicated byreference numeral 94; high speed, higher displacement configurationsimilar to that of FIG. 4 in the region of the plot indicated byreference numeral 96; and high speed, reduced displacement configurationsimilar to that of FIG. 5 in the region of the plot indicated byreference numeral 100.

As is apparent, the shaded area between the engine demand curve and theoutput curve of system 20, wherein energy is lost as the output ofsystem 20 exceeds engine demand, is much smaller than the comparableregion of FIG. 1.

While in the embodiments of system 20 illustrated above control chamber72 and chamber 68 are supplied with pressurized “clean” lubrication oildownstream of oil filter 60, it will be apparent to those of skill inthe art that the present invention is not so limited and either or bothof control chamber 72 and chamber 68 can be supplied with pressurizedlubricating oil from a point prior to oil filter 60, as illustrated inFIG. 7 wherein like components to those of FIGS. 2 through 5 areindicated with like reference numerals.

As illustrated in FIG. 8, wherein like components to those of FIGS. 2through 5 are indicated with like reference numerals, the presentinvention is not limited to control valve 76 being in fluidcommunication with control chamber 72 and chamber 68 being in fluidcommunication with a supply of pressurized lubricating oil. Instead, asillustrated in FIG. 8, control valve 76 can be used to control thesupply of pressurized lubricating oil to chamber 68 while controlchamber 72 is directly connected to a supply of pressurized lubricatingoil.

It is further contemplated that, for any of the configurations of FIGS.2 through 5 and FIG. 7 or 8 control valve 76 can be a variable orificevalve which can control the pressure of the lubrication oil supplied tocontrol chamber 72, rather than just connect chamber 72 to thelubrication oil pressurized by VDVP 24 or return line 78. In thismanner, a pump output characteristic can be obtained, under propercontrol by the ECU or other suitable control means, which very closelycorresponds to the requirements of the engine rather than just twodistinct pressure settings.

Another embodiment of a lubrication pump system in accordance with thepresent invention is indicated generally at 200 in FIG. 9, wherein likecomponents to those of system 20 are indicated with like referencenumerals. In system 200, VDVP 204 includes a pair of control cylinders208 and 212, preferably of different diameters and thus having differentareas, each of which has a respective chamber 216 and 220 which can beconnected to a supply of pressurized lubrication oil by a two portcontrol valve 224 while control chamber 72 is in direct fluidcommunication with the pressurized lubrication oil pressurized by VDVP204. In the illustrated embodiment, control piston 208 has a largercross sectional area than control piston 212, thus producing a greaterforce for a given pressure of pressurized lubrication oil. This allowsfor a finer granularity of control of the output of VDVP 204.

Control valve 224 can be operated by the ECU, or any other suitablecontrol means, to supply neither or either of chambers 216 and 220 withpressurized lubrication oil and/or to connect either or both chambers216 and 220 to source 52, via return line 78. If neither of chambers 216or 220 are supplied with pressurized lubrication oil, the force createdby the pressurized lubrication oil in control chamber 72 is the onlyforce acting on control slider 36 against the biasing force of biasingspring 44. If one of chambers 216 and 220 is supplied with pressurizedlubrication oil, then the forced developed on the respective one ofcontrol cylinders 208 and 212 adds to the force developed by controlchamber 72. As will now be apparent, system 200 allows the outputcharacteristic of VDVP 204 to more closely match the requirements of theengine.

While the embodiment of FIG. 9 shows only one configuration for a VDVPsystem 200 with three selectable pressures and, as should now beapparent to those of skill in the art, different configurations andor/types of valve 224 can be employed to accommodate different VDVPoutput requirements.

FIG. 10 shows a plot, similar to that of FIG. 1, of the lubricating oilpressure requirement (shown in solid line) of a typical internalcombustion engine versus the output (shown in dashed line) of system200. When the engine is at low speeds, control valve 224 is opened sothat the larger chamber 216 is supplied with pressurized lubrication oiland thus each of control chamber 72 and control cylinder 208 can applyforce to control slider 36.

The transition point labeled “A” in the plot corresponds to the pressureof the lubrication oil output by VDVP 204 reaching the point wherein thesum of the resulting forces from control chamber 72 and control cylinder208 is sufficient to begin moving control slider 36 against the biasingforce of biasing spring 44.

The transition point labeled “B” in the plot corresponds to controlvalve 224 removing the supply of pressurized lubrication oil fromchamber 216 and adding the supply of oil to control chamber 220 thuscontrol chamber 72 and control cylinder 212 then apply force to controlslider 36.

The transition point labeled “C” in the plot corresponds to controlvalve 224 also removing the supply of pressurized lubrication oil fromchamber 220 and thus only control chamber 72 then applies force tocontrol slider 36.

As is apparent, the shaded area between the engine demand curve and theoutput curve of system 200, wherein energy is lost as the output ofsystem 200 exceeds engine demand, is much smaller than the comparableregions of FIGS. 1 and 6.

Another embodiment of a lubrication pump system in accordance with thepresent invention is indicated generally at 300 in FIG. 11 wherein likecomponents to those of system 20 and/or system 200 are indicated withlike reference numerals. In system 300, VDVP 304 is not equipped with acontrol chamber 72 and, instead, volume 304 is maintained atsubstantially atmospheric pressure, similar to volume 80 as there is noslide seal in this embodiment. However, chamber 224 is connecteddirectly to a supply of pressurized lubrication oil and, along withcontrol cylinder 208, provides force to control slider 36 in the mannerof control cylinder 44 of FIGS. 2 through 5 or in the manner of controlchamber 72 of FIG. 7. Chamber 220 is connected to control valve 76 and,when connected by control valve 76 to a source of pressurizedlubricating oil, applies force to control slider 36 via control cylinder212.

Another embodiment of a lubrication pump system in accordance with thepresent invention is indicated generally at 400 in FIG. 12, wherein likecomponents to those of system 20 are indicated with like referencenumerals. In system 400, VDVP 404 includes a double acting controlcylinder 408 and a first control chamber 412 and a second controlchamber 416. Second control chamber 412 has a smaller projected area oncontrol cylinder 408 than does control chamber 416.

Control chamber 416 is connected directly to a supply of pressurizedlubrication oil while control chamber 412 can be connected to the samesupply of pressurized lubrication oil via control valve 420. As shown inthe Figure, control valve 420 is operable to either connect controlchamber 412 to the above-mentioned supply of pressurized lubrication oilor to connect chamber 412 to source 52, to allow pressurized lubricationoil to leave control chamber 412 and return to source 52.

As will now be apparent, pressurized lubrication oil in control chamber416 generates a force on control cylinder 408 which acts against biasingspring 40 to move control slide 36 to decrease the displacement of VDVP404. However, when control valve 420 allows pressurized lubrication oilto enter control chamber 412, the force developed on control cylinder408 in control chamber 412 adds to the force of biasing spring 40 tooppose the force generated in control chamber 416 on control cylinder408. By appropriately operating control valve 420, the output of VDVP404 can be more closely matched to the requirements of the engine.

Another embodiment of a lubrication pump system in accordance with thepresent invention is indicated generally at 500 in FIG. 13, wherein likecomponents to those of system 20 are indicated with like referencenumerals. In system 500, VDVP 504 includes a control cylinder 508 and afirst control chamber 512 and a second control chamber 516. Secondcontrol chamber 516 is directly connected to a supply of pressurizedlubrication oil while control chamber 72 and first control chamber 512can selectively be connected to the supply of pressurized lubricationoil or to a return line to source 52 via control valve 520. Asillustrated, and unlike the embodiment of FIG. 12 discussed above, theforces produced in first control chamber 512 and second control chamber516 both act on control cylinder 508 to counter the force of biasingspring 40 on control slide 36 as does the force on control slide 36produced in chamber 72.

As will now be apparent, the output of system 500 can be adjustedbetween three states, allowing control of the output of system 500 withrelatively fine granularity. Specifically, the three states are achievedby pressurizing: second control chamber 516; second control chamber 516and chamber 72 (by moving control valve 520 to connect chamber 72 to thesupply of pressurized lubricating oil); second control chamber 516 andfirst control chamber 512 (by moving control valve 520 to connect firstcontrol chamber 512 to the supply of pressurized lubricating oil). Asthe projected area of chamber 72 differs from the area of first controlchamber 512, and in the illustrated embodiment the projected area ofchamber 72 is larger than the area of first control chamber 512, theabove described embodiment provides three stages of output for system500.

Further, in case of a failure of the control signals from the ECU, orcontrol valve 520 itself, assumes a centered position wherein chamber 72and first control chamber 512 are connected to source 52 by theirrespective return lines, ensuring that system 500 assumes its maximumdisplacement operating state as a failsafe configuration. As will beapparent to those of skill in the art, similar failsafe configurationscan be provided for the other embodiments described above.

The present invention provides a variable displacement variable pressurevane pump system for providing lubrication oil to internal combustionengines. The system includes at least a first control mechanism, whichcan be a control chamber directly acting on the control slider or acontrol chamber and control cylinder which acts on the control sliderand a second control mechanism which is a control chamber and controlcylinder which acts on the control slider. A control valve, operated bythe engine control unit or other suitable control mechanism, canselectively apply or remove pressurized lubrication oil to the secondcontrol mechanism to allow the output of the pump system to more closelymatch the requirements of the engine. In one embodiment, the controlmechanism merely applies or removes pressurized lubrication oil and inanother embodiment, the control mechanism can control the pressure ofthe pressurized lubrication oil provided to the second controlmechanism. In another embodiment a third control mechanism, which is acontrol chamber and control cylinder which acts on the control slider,is provided to provide finer granularity in controlling the output ofthe pump system to more closely correspond to the lubricationrequirements of the engine. In yet another embodiment, both the firstand second control mechanisms are control chambers and control cylinderswhich act on the control slider.

While the embodiments illustrated above show scenarios wherein the ECU,or other means, is providing a simple control signal that has two orthree conditions related to engine speed, it will be apparent to thoseof skill in the art, that the control signal provided can be related toother parameters such as: temperature; the use of piston cooling jets;or a combination of parameters programmed into the ECU or other controlprocessor or device. In all those scenarios, the principle of varyingthe pump capacity as well as pump pressure output is the same as thatdescribed herein.

The above-described embodiments of the invention are intended to beexamples of the present invention and alterations and modifications maybe effected thereto, by those of skill in the art, without departingfrom the scope of the invention which is defined solely by the claimsappended hereto.

We claim:
 1. A variable displacement variable pressure vane pump systemfor providing lubrication oil to a mechanical system comprises: avariable displacement variable pressure vane pump having a controlslider which is moveable to alter the displacement of the pump; abiasing means to bias the control slider towards a positioncorresponding to the maximum displacement position of the pump; a firstcontrol mechanism responsive to the pressure of the lubrication oiloutput from the pump to apply a force to the control slider to counterthe biasing force of the biasing means and to urge the control slideraway from the position corresponding to the maximum displacementposition of the pump; a second control mechanism responsive to thepressure of the lubrication oil output from the pump to apply a force tothe control slider to alter the displacement of the pump; and a controlmeans operable to vary the lubrication oil supplied to the secondcontrol mechanism to alter the output of the pump to more closelycorrespond to the lubrication requirements of the mechanical system. 2.The variable displacement variable pressure pump system of claim 1wherein the first control mechanism comprises a control chamber formedbetween the exterior of the control slider, a control slider seal, acontrol slider pivot point and the interior surface of the housing ofthe pump, the pressurized lubricating oil provided to the controlchamber directly producing the force on the control slider.
 3. Thevariable displacement variable pressure pump system of claim 2 whereinthe control means comprises a solenoid valve.
 4. The variabledisplacement variable pressure pump system of claim 3 wherein thesolenoid valve is electrically controlled by an engine control unit. 5.The variable displacement variable pressure pump system of claim 3wherein the solenoid valve is operable to alter the pressure of thepressurized lubrication oil provided to the second control mechanism. 6.The variable displacement variable pressure pump system of claim 1wherein the first and second control mechanisms each comprise chambersand control cylinders.
 7. The variable displacement variable pressurepump system of claim 1 further including a third control mechanismresponsive to the pressure of the lubrication oil output from the pumpto apply a force to the control slider to counter the biasing force ofthe biasing means and to urge the control slider away from the positioncorresponding to the maximum displacement position of the pump andwherein the control means is operable to vary the lubrication oil outputfrom either or both of the second control mechanism and the thirdcontrol mechanism to alter the output of the pump to more closelycorrespond to the lubrication requirements of the mechanical system. 8.The variable displacement variable pressure pump system of claim 1wherein the mechanical system is an internal combustion engine.
 9. Thevariable displacement variable pressure pump system of claim 1 whereinthe mechanical system is an automatic transmission.
 10. The variabledisplacement variable pressure pump system of claim 1 wherein thepressurized lubrication oil is supplied to the first and second controlmeans from the outlet of the pump.
 11. The variable displacementvariable pressure pump system of claim 1 wherein the pressurizedlubrication oil is supplied to the first and second control means from alubrication oil gallery of the mechanical system.
 12. The variabledisplacement variable pressure pump system of claim 1 wherein the forceapplied to the control slider by the second control mechanism countersthe force applied to the control slider by the first control mechanism.13. The variable displacement variable pressure pump system of claim 1further comprising a third control mechanism responsive to the pressureof the lubrication oil output from the pump to apply a force to thecontrol slider to counter the biasing force of the biasing means and tourge the control slider away from the position corresponding to themaximum displacement position of the pump and wherein the control meansis further operable to vary the supply of lubrication oil between thesecond control mechanism and the third control mechanism to alter theoutput of the pump to more closely correspond to the lubricationrequirements of the mechanical system and wherein the second controlmechanism and the third control mechanism create different magnitudes offorce for a given pressure of lubrication oil.